Synthesis gas, source for the large scale production of synthetic fuels including methanol, DME (dimethyl ether) and other varied hydrocarbons and their products. Industrially synthesis gas is produced form steam reforming of methane. Synthesis gas is a variable composition of carbon monoxide and hydrogen and is the basis of Fischer-Tropsch chemistry. Synthesis gas can be produced by other processes like partial oxidation of methane, dry reforming of methane, autothermal reforming of methane, bi-reforming of methane, tri-reforming of methane. By these processes a variable composition of carbon monoxide and hydrogen can be produced.
Methanol and its derivatives are significant fuels and starting materials for varied chemical products. The current production of methanol is based on syngas following a process first developed by Mittasch et. al. in 1923 and then improved over the years by companies including BASF and ICI. However, the need for a wider use of methanol is a more efficient and economic pathway of preparation.
The main requirement for the synthesis of methanol from syngas is the ratio of H2/CO of 2. The most commonly and industrially used method for the synthesis gas production is steam reforming of methane. But steam reforming of methane produces H2/CO ratio of 3. Therefore, it is evident that additional steps are required to get the desired H2/CO ratio for the methanol production. Now, dry reforming or carbon dioxide reforming of methane produces H2/CO ratio 1. So, extra hydrogen has to be supplied for the desired H2/CO ratio to produce methanol. Partial oxidation of methane is a process where we can get the exact required H2/CO ratio for the production of methanol. But the main problem with the partial oxidation is it is difficult to control and can lead to hot spot generation which can be dangerous and increases the possibility of explosions.
Now, tri-reforming of methane is a very new idea for the production of synthesis gas with variable H2/CO ratio. The H2/CO ratio can be varied by using different ratios of feed gas. We can get the exact H2/CO ratio 2 by maintaining a definite ratio of feed gas. This specific ratio of H2/CO of synthesis gas is named as “met gas” to underline its difference from the widely used synthesis gas. This specific 2/1 ratio of H2/CO gas mixture is for the preparation of methanol with complete utilization of all the hydrogen.
Tri-reforming of methane combines three processes for the production of synthesis gas, (1) Partial oxidation of methane, (2) Dry or carbon dioxide reforming of methane and (3) steam reforming of methane. In this process three reactions runs simultaneously to produce synthesis gas. Both dry and steam reforming are endothermic reactions whereas partial oxidation is an exothermic reaction. Therefore the heat generated in partial oxidation can be utilized with no loss of heat. The partial oxidation of methane also produces CO2 and H2O which also can be utilized during the reaction without any loss of reaction feed. These advantages makes this process quit economic and energy saving.
For the reforming processes Ni based catalysts are mostly studied for its activity and availability. But the main problem of nickel based catalysts is its tendency towards coking during the reaction which leads to hot spot generation and it can lead to explosion. Noble metal based catalysts are also very reactive and coke resistant but the cost and the availability makes their used bounded.
Reforming is frequently affected by coking, involving the deposition of carbon in the form of soot or coke on the catalyst bed (reducing strongly its activity. Carbon may be formed by both CH4 (natural gas) decomposition and CO disproportionation (Boudouard reaction). The relative contributions depend on the reaction conditions and catalyst used. The undesired formation of carbon is, however, largely prevented by the presence of steam and short residence times in the flow reactor.
Joseph Wood et. al. reported in International Journal of Hydrogen Energy (2014), 39(24), 12578-12585, use of Ni@SiO2 catalyst for tri-reforming of methane. They reported 71.2 and 63.0 methane and CO2 conversion at 750° C. with CH4:CO2:H2O:O2:He feed ratio 1:0.5:1.0:0.1:0.4 and the drawback of the report is the catalyst stability. The catalyst shows deactivation after 4 hours' time.
Chunshan Song and Wei Pan reported in Prepr. Pap.-Am. Chem. Soc., Div. Fuel Chem. 2004, 49 (1), 128 use of different catalysts like Ni—MgO, Ni—CeO2, Ni—ZrO2, Ni—CeZrO2, Ni—MgO—CeZrO2 etc. with CH4:CO2:H2O:O2 feed ratio=1:0.475:0.475:0.1 at 850° C. under 1 atm. and the maximum conversion showed is 98.5, 84.5 for methane and CO2 respectively over Ni—MgO catalyst.
Jesus Manuel Garcia-Vargas et. al. reported in International Journal of Hydrogen Energy (2013), 38(11), 4524-4532, use of Ni/β-siC-based catalyst for the tri-reforming of methane. They reported 95.9% methane conversion at 800° C.
Tracy J Benson presented at Symposia-American Chemical Society, Division of Fuel Chemistry (2012), 57(1), 839-840 use of Ni catalyst supported on titanium oxide.
In Applied Catalysis, B: Environmental (2011), 104(1-2), 64-73 where Lidia Pino et. al. reported tri-reforming of methane over Ni—CeO2 catalysts with different La loadings at 800° C. with CH4 and CO2 conversion of 96% and 86.5% respectively.
In Reaction Kinetics, Mechanisms and Catalysis, Volume 101, Issue 2, Pages 407-416 where Leonardo J. L. Maciel et. al. reported conversion of methane and carbon dioxide with Ni/γ-Al2O3 catalyst at 727° C.
Joseph Wood reported in International Journal of Hydrogen Energy (2014), 39(24), 12578-12585 where use of Ni@SiO2 core shell catalyst for the tri-reforming of methane. They reported 71.2% and 63.0% methane and CO2 conversion at 750° C. with CH4:CO2:H2O:O2:He feed ratio 1:0.5:1.0:0.1:0.4 and the drawback of the report is the catalyst stability. The catalyst shows deactivation after 4 hours.